I've got one that has been in near constant use since the late '80s.
It's a little tatty now, the elastic around the lid has gone, and the waterproof coating on the inside of the pack is a bit flakey, bit other than that it's in great condition.
It has what Karrimor called the SA Back System, which means "Size Adjustable".
It's a great system which allows you to move the back pad up and down while wearing the pack.
It runs on a couple of aluminium stays that form the frame, which can be bent to shape.